The more people there are in a room, the louder you will have to speak. People make noise unintentionally by moving around in their seats or shuffling papers.
If you find that you have to shout to make yourself heard in the back of the room, then you need a microphone. Overall, though, conference rooms tend to be built in order to allow a presenter’s voice to carry. The difficulty of getting your voice to just the right volume for a presentation is made by the fact that there are multiple rows of people viewing the presentation. In this case, it is important to take account of the seating arrangements.
Before you say anything else in a presentation, it may be a good idea to ask, in the voice you intend to use for the presentation, whether everyone can hear you clearly. The element of balance is again important here.
Speakers who are too quiet will have the obvious disadvantage that their listeners genuinely cannot hear them, as well as the fact that they will appear nervous and not in command. This does not excuse going too far in the opposite direction, which will lead people to consider you brash and over-confident, and either consciously or subconsciously give less weight to your views.
Shouting distorts the voice, and it is a simple fact that something which is shouted will not be heard as clearly as something of a similar length which is spoken powerfully from the middle of the chest. Also bear in mind that if you plan to move around the venue, you will need to make adjustments at times to ensure that your voice carries the extra distance.
If you are facing away from the audience, keep your statements during this time to a minimum, and try if possible to turn to face them during this period. If a microphone will be necessary, ensure that one is available, and tested before use – microphones can have a distorting effect which will make any presentation less worthwhile.